(1) Field of the Invention
The present invention relates to a brake for vehicles, particularly suitable for light vehicles such as bicycles.
(2) Description of the Prior Art
Various brakes for vehicles have been proposed such as expanding drum brakes, contracting band brakes, disc brakes and the like. The expanding drum brake comprises brake shoes adapted to be urged against an inside of a drum, so that the drum is subjected to forces on the side and hence required to have thicker walls having a high strength to support such forces acting upon on one side thereof. As the result, the weight of the drum becomes unavoidably heavier and therefore the brake itself becomes larger. In general, furthermore, such an expanding drum brake is inferior in dissipation of heat caused by the braking action and often cannot be used for a long period of time.
The contracting band brake of the prior art comprises a lining covering substantially all of a drum, so that it is also disadvantageous in dissipation of heat.
The disc brake of the prior art inherently does not have a constuction adapted to cause "self-energizing" action (servo effect). The self-energizing action used herein means the effect that a frictional force between a brake shoe and a rotating drum tends to force the brake shoe against the drum to increase the braking function. As the disc brake does not have such a self-energizing action, a great operating force for braking is required to obtain enough braking force. In order to decrease the great operating force, a brake disc must be larger in diameter which would make the brake larger.